Piezoelectric micromachined ultrasonic transducer (pmut)

ABSTRACT

A Piezoelectric Micromachined Ultrasonic Transducer (PMUT) device is provided. The PMUT includes a substrate and an edge support structure connected to the substrate. A membrane is connected to the edge support structure such that a cavity is defined between the membrane and the substrate, where the membrane is configured to allow movement at ultrasonic frequencies. The membrane includes a piezoelectric layer and first and second electrodes coupled to opposing sides of the piezoelectric layer. An interior support structure is disposed within the cavity and connected to the substrate and the membrane.

RELATED APPLICATIONS

This application claims priority to, is a continuation of, and claimsthe benefit of co-pending U.S. non-Provisional patent application Ser.No. 15/205,743, filed on Jul. 8, 2016, entitled “A PIEZOELECTRICMICROMACHINED ULTRASONIC TRANSDUCER (PMUT),” by Ng et al., havingAttorney Docket No. IVS-681, and assigned to the assignee of the presentapplication, which is herein incorporated by reference in its entirety.

U.S. non-Provisional patent application Ser. No. 15/205,743 claimspriority to and the benefit of then co-pending U.S. Patent ProvisionalPatent Application 62/331,919, filed on May 4, 2016, entitled “PINNEDULTRASONIC TRANSDUCERS,” by Ng et al., having Attorney Docket No.IVS-681.PR, and assigned to the assignee of the present application,which is incorporated herein by reference in its entirety.

BACKGROUND

Piezoelectric materials facilitate conversion between mechanical energyand electrical energy. Moreover, a piezoelectric material can generatean electrical signal when subjected to mechanical stress, and canvibrate when subjected to an electrical voltage. Piezoelectric materialsare widely utilized in piezoelectric ultrasonic transducers to generateacoustic waves based on an actuation voltage applied to electrodes ofthe piezoelectric ultrasonic transducer.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe Description of Embodiments, illustrate various embodiments of thesubject matter and, together with the Description of Embodiments, serveto explain principles of the subject matter discussed below. Unlessspecifically noted, the drawings referred to in this Brief Descriptionof Drawings should be understood as not being drawn to scale. Herein,like items are labeled with like item numbers.

FIG. 1 is a diagram illustrating a PMUT device having a center pinnedmembrane, according to some embodiments.

FIG. 2 is a diagram illustrating an example of membrane movement duringactivation of a PMUT device, according to some embodiments.

FIG. 3 is a top view of the PMUT device of FIG. 1, according to someembodiments.

FIG. 4 is a simulated map illustrating maximum vertical displacement ofthe membrane of the PMUT device shown in FIGS. 1-3, according to someembodiments.

FIG. 5 is a top view of an example PMUT device having a circular shape,according to some embodiments.

FIG. 6 is a top view of an example PMUT device having a hexagonal shape,according to some embodiments.

FIG. 7 illustrates an example array of circular-shaped PMUT devices,according to some embodiments.

FIG. 8 illustrates an example array of square-shaped PMUT devices,according to some embodiments.

FIG. 9 illustrates an example array of hexagonal-shaped PMUT devices,according to some embodiments.

FIG. 10 illustrates an example pair of PMUT devices in a PMUT array,with each PMUT having differing electrode patterning, according to someembodiments.

FIGS. 11A, 11B, 11C, and 11D illustrate alternative examples of interiorsupport structures, according to various embodiments.

FIG. 12 illustrates a PMUT array used in an ultrasonic fingerprintsensing system, according to some embodiments.

FIG. 13 illustrates an integrated fingerprint sensor formed by waferbonding a CMOS logic wafer and a microelectromechanical (MEMS) waferdefining PMUT devices, according to some embodiments.

DESCRIPTION OF EMBODIMENTS

The following Description of Embodiments is merely provided by way ofexample and not of limitation. Furthermore, there is no intention to bebound by any expressed or implied theory presented in the precedingbackground or in the following Description of Embodiments.

Reference will now be made in detail to various embodiments of thesubject matter, examples of which are illustrated in the accompanyingdrawings. While various embodiments are discussed herein, it will beunderstood that they are not intended to limit to these embodiments. Onthe contrary, the presented embodiments are intended to coveralternatives, modifications and equivalents, which may be includedwithin the spirit and scope the various embodiments as defined by theappended claims. Furthermore, in this Description of Embodiments,numerous specific details are set forth in order to provide a thoroughunderstanding of embodiments of the present subject matter. However,embodiments may be practiced without these specific details. In otherinstances, well known methods, procedures, components, and circuits havenot been described in detail as not to unnecessarily obscure aspects ofthe described embodiments.

Notation and Nomenclature

Some portions of the detailed descriptions which follow are presented interms of procedures, logic blocks, processing and other symbolicrepresentations of operations on data within an electrical device. Thesedescriptions and representations are the means used by those skilled inthe data processing arts to most effectively convey the substance oftheir work to others skilled in the art. In the present application, aprocedure, logic block, process, or the like, is conceived to be one ormore self-consistent procedures or instructions leading to a desiredresult. The procedures are those requiring physical manipulations ofphysical quantities. Usually, although not necessarily, these quantitiestake the form of acoustic (e.g., ultrasonic) signals capable of beingtransmitted and received by an electronic device and/or electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated in an electrical device.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise as apparent from the followingdiscussions, it is appreciated that throughout the description ofembodiments, discussions utilizing terms such as “transmitting,”“receiving,” “sensing,” “generating,” “imaging,” or the like, refer tothe actions and processes of an electronic device such as an electricaldevice.

Embodiments described herein may be discussed in the general context ofprocessor-executable instructions residing on some form ofnon-transitory processor-readable medium, such as program modules,executed by one or more computers or other devices. Generally, programmodules include routines, programs, objects, components, datastructures, etc., that perform particular tasks or implement particularabstract data types. The functionality of the program modules may becombined or distributed as desired in various embodiments.

In the figures, a single block may be described as performing a functionor functions; however, in actual practice, the function or functionsperformed by that block may be performed in a single component or acrossmultiple components, and/or may be performed using hardware, usingsoftware, or using a combination of hardware and software. To clearlyillustrate this interchangeability of hardware and software, variousillustrative components, blocks, modules, logic, circuits, and stepshave been described generally in terms of their functionality. Whethersuch functionality is implemented as hardware or software depends uponthe particular application and design constraints imposed on the overallsystem. Skilled artisans may implement the described functionality invarying ways for each particular application, but such implementationdecisions should not be interpreted as causing a departure from thescope of the present disclosure. Also, the example fingerprint sensingsystem and/or mobile electronic device described herein may includecomponents other than those shown, including well-known components.

Various techniques described herein may be implemented in hardware,software, firmware, or any combination thereof, unless specificallydescribed as being implemented in a specific manner. Any featuresdescribed as modules or components may also be implemented together inan integrated logic device or separately as discrete but interoperablelogic devices. If implemented in software, the techniques may berealized at least in part by a non-transitory processor-readable storagemedium comprising instructions that, when executed, perform one or moreof the methods described herein. The non-transitory processor-readabledata storage medium may form part of a computer program product, whichmay include packaging materials.

The non-transitory processor-readable storage medium may comprise randomaccess memory (RAM) such as synchronous dynamic random access memory(SDRAM), read only memory (ROM), non-volatile random access memory(NVRAM), electrically erasable programmable read-only memory (EEPROM),FLASH memory, other known storage media, and the like. The techniquesadditionally, or alternatively, may be realized at least in part by aprocessor-readable communication medium that carries or communicatescode in the form of instructions or data structures and that can beaccessed, read, and/or executed by a computer or other processor.

Various embodiments described herein may be executed by one or moreprocessors, such as one or more motion processing units (MPUs), sensorprocessing units (SPUs), host processor(s) or core(s) thereof, digitalsignal processors (DSPs), general purpose microprocessors, applicationspecific integrated circuits (ASICs), application specific instructionset processors (ASIPs), field programmable gate arrays (FPGAs), aprogrammable logic controller (PLC), a complex programmable logic device(CPLD), a discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein, or other equivalent integrated or discrete logiccircuitry. The term “processor,” as used herein may refer to any of theforegoing structures or any other structure suitable for implementationof the techniques described herein. As it employed in the subjectspecification, the term “processor” can refer to substantially anycomputing processing unit or device comprising, but not limited tocomprising, single-core processors; single-processors with softwaremultithread execution capability; multi-core processors; multi-coreprocessors with software multithread execution capability; multi-coreprocessors with hardware multithread technology; parallel platforms; andparallel platforms with distributed shared memory. Moreover, processorscan exploit nano-scale architectures such as, but not limited to,molecular and quantum-dot based transistors, switches and gates, inorder to optimize space usage or enhance performance of user equipment.A processor may also be implemented as a combination of computingprocessing units.

In addition, in some aspects, the functionality described herein may beprovided within dedicated software modules or hardware modulesconfigured as described herein. Also, the techniques could be fullyimplemented in one or more circuits or logic elements. A general purposeprocessor may be a microprocessor, but in the alternative, the processormay be any conventional processor, controller, microcontroller, or statemachine. A processor may also be implemented as a combination ofcomputing devices, e.g., a combination of an SPU/MPU and amicroprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with an SPU core, MPU core, or any othersuch configuration.

Overview of Discussion

Discussion begins with a description of an example piezoelectricmicromachined ultrasonic transducer (PMUT), in accordance with variousembodiments. Example arrays including PMUT devices are then described.Example operations of the example arrays of PMUT devices are thenfurther described.

A conventional piezoelectric ultrasonic transducer able to generate anddetect pressure waves can include a membrane with the piezoelectricmaterial, a supporting layer, and electrodes combined with a cavitybeneath the electrodes. Miniaturized versions are referred to as PMUTs.Typical PMUTs use an edge anchored membrane or diaphragm that maximallyoscillates at or near the center of the membrane at a resonant frequency(f) proportional to h/a², where h is the thickness, and a is the radiusof the membrane. Higher frequency membrane oscillations can be createdby increasing the membrane thickness, decreasing the membrane radius, orboth. Increasing the membrane thickness has its limits, as the increasedthickness limits the displacement of the membrane. Reducing the PMUTmembrane radius also has limits, because a larger percentage of PMUTmembrane area is used for edge anchoring.

Embodiments describes herein relate to a PMUT device for ultrasonic wavegeneration and sensing. In accordance with various embodiments, an arrayof such PMUT devices is described. The PMUT includes a substrate and anedge support structure connected to the substrate. A membrane isconnected to the edge support structure such that a cavity is definedbetween the membrane and the substrate, where the membrane is configuredto allow movement at ultrasonic frequencies. The membrane includes apiezoelectric layer and first and second electrodes coupled to opposingsides of the piezoelectric layer. An interior support structure isdisposed within the cavity and connected to the substrate and themembrane.

The described PMUT device and array of PMUT devices can be used forgeneration of acoustic signals or measurement of acoustically senseddata in various applications, such as, but not limited to, medicalapplications, security systems, biometric systems (e.g., fingerprintsensors and/or motion/gesture recognition sensors), mobile communicationsystems, industrial automation systems, consumer electronic devices,robotics, etc. In one embodiment, the PMUT device can facilitateultrasonic signal generation and sensing (transducer). Moreover,embodiments describe herein provide a sensing component including asilicon wafer having a two-dimensional (or one-dimensional) array ofultrasonic transducers.

Embodiments described herein provide a PMUT that operates at a highfrequency for reduced acoustic diffraction through high acousticvelocity materials (e.g., glass, metal), and for shorter pulses so thatspurious reflections can be time-gated out. Embodiments described hereinalso provide a PMUT that has a low quality factor providing a shorterring-up and ring-down time to allow better rejection of spuriousreflections by time-gating. Embodiments described herein also provide aPMUT that has a high fill-factor providing for large transmit andreceive signals.

Piezoelectric Micromachined Ultrasonic Transducer (PMUT)

Systems and methods disclosed herein, in one or more aspects provideefficient structures for an acoustic transducer (e.g., a piezoelectricactuated transducer or PMUT). One or more embodiments are now describedwith reference to the drawings, wherein like reference numerals are usedto refer to like elements throughout. In the following description, forpurposes of explanation, numerous specific details are set forth inorder to provide a thorough understanding of the various embodiments. Itmay be evident, however, that the various embodiments can be practicedwithout these specific details. In other instances, well-knownstructures and devices are shown in block diagram form in order tofacilitate describing the embodiments in additional detail.

As used in this application, the term “or” is intended to mean aninclusive “or” rather than an exclusive “or”. That is, unless specifiedotherwise, or clear from context, “X employs A or B” is intended to meanany of the natural inclusive permutations. That is, if X employs A; Xemploys B; or X employs both A and B, then “X employs A or B” issatisfied under any of the foregoing instances. In addition, thearticles “a” and “an” as used in this application and the appendedclaims should generally be construed to mean “one or more” unlessspecified otherwise or clear from context to be directed to a singularform. In addition, the word “coupled” is used herein to mean direct orindirect electrical or mechanical coupling. In addition, the word“example” is used herein to mean serving as an example, instance, orillustration.

FIG. 1 is a diagram illustrating a PMUT device 100 having a centerpinned membrane, according to some embodiments. PMUT device 100 includesan interior pinned membrane 120 positioned over a substrate 140 todefine a cavity 130. In one embodiment, membrane 120 is attached both toa surrounding edge support 102 and interior support 104. In oneembodiment, edge support 102 is connected to an electric potential. Edgesupport 102 and interior support 104 may be made of electricallyconducting materials, such as and without limitation, aluminum,molybdenum, or titanium. Edge support 102 and interior support 104 mayalso be made of dielectric materials, such as silicon dioxide, siliconnitride or aluminum oxide that have electrical connections the sides orin vias through edge support 102 or interior support 104, electricallycoupling lower electrode 106 to electrical wiring in substrate 140.

In one embodiment, both edge support 102 and interior support 104 areattached to a substrate 140. In various embodiments, substrate 140 mayinclude at least one of, and without limitation, silicon or siliconnitride. It should be appreciated that substrate 140 may includeelectrical wirings and connection, such as aluminum or copper. In oneembodiment, substrate 140 includes a CMOS logic wafer bonded to edgesupport 102 and interior support 104. In one embodiment, the membrane120 comprises multiple layers. In an example embodiment, the membrane120 includes lower electrode 106, piezoelectric layer 110, and upperelectrode 108, where lower electrode 106 and upper electrode 108 arecoupled to opposing sides of piezoelectric layer 110. As shown, lowerelectrode 106 is coupled to a lower surface of piezoelectric layer 110and upper electrode 108 is coupled to an upper surface of piezoelectriclayer 110. It should be appreciated that, in various embodiments, PMUTdevice 100 is a microelectromechanical (MEMS) device.

In one embodiment, membrane 120 also includes a mechanical support layer112 (e.g., stiffening layer) to mechanically stiffen the layers. Invarious embodiments, mechanical support layer 140 may include at leastone of, and without limitation, silicon, silicon oxide, silicon nitride,aluminum, molybdenum, titanium, etc. In one embodiment, PMUT device 100also includes an acoustic coupling layer 114 above membrane 120 forsupporting transmission of acoustic signals. It should be appreciatedthat acoustic coupling layer can include air, liquid, gel-likematerials, or other materials for supporting transmission of acousticsignals. In one embodiment, PMUT device 100 also includes platen layer116 above acoustic coupling layer 114 for containing acoustic couplinglayer 114 and providing a contact surface for a finger or other sensedobject with PMUT device 100. It should be appreciated that, in variousembodiments, acoustic coupling layer 114 provides a contact surface,such that platen layer 116 is optional. Moreover, it should beappreciated that acoustic coupling layer 114 and/or platen layer 116 maybe included with or used in conjunction with multiple PMUT devices. Forexample, an array of PMUT devices may be coupled with a single acousticcoupling layer 114 and/or platen layer 116.

FIG. 2 is a diagram illustrating an example of membrane movement duringactivation of PMUT device 100, according to some embodiments. Asillustrated with respect to FIG. 2, in operation, responsive to anobject proximate platen layer 116, the electrodes 106 and 108 deliver ahigh frequency electric charge to the piezoelectric layer 110, causingthose portions of the membrane 120 not pinned to the surrounding edgesupport 102 or interior support 104 to be displaced upward into theacoustic coupling layer 114. This generates a pressure wave that can beused for signal probing of the object. Return echoes can be detected aspressure waves causing movement of the membrane, with compression of thepiezoelectric material in the membrane causing an electrical signalproportional to amplitude of the pressure wave.

The described PMUT device 100 can be used with almost any electricaldevice that converts a pressure wave into mechanical vibrations and/orelectrical signals. In one aspect, the PMUT device 100 can comprise anacoustic sensing element (e.g., a piezoelectric element) that generatesand senses ultrasonic sound waves. An object in a path of the generatedsound waves can create a disturbance (e.g., changes in frequency orphase, reflection signal, echoes, etc.) that can then be sensed. Theinterference can be analyzed to determine physical parameters such as(but not limited to) distance, density and/or speed of the object. As anexample, the PMUT device 100 can be utilized in various applications,such as, but not limited to, fingerprint or physiologic sensors suitablefor wireless devices, industrial systems, automotive systems, robotics,telecommunications, security, medical devices, etc. For example, thePMUT device 100 can be part of a sensor array comprising a plurality ofultrasonic transducers deposited on a wafer, along with various logic,control and communication electronics. A sensor array may comprisehomogenous or identical PMUT devices 100, or a number of different orheterogonous device structures.

In various embodiments, the PMUT device 100 employs a piezoelectriclayer 110, comprised of materials such as, but not limited to, Aluminumnitride (AlN), lead zirconate titanate (PZT), quartz, polyvinylidenefluoride (PVDF), and/or zinc oxide, to facilitate both acoustic signalproduction and sensing. The piezoelectric layer 110 can generateelectric charges under mechanical stress and conversely experience amechanical strain in the presence of an electric field. For example, thepiezoelectric layer 110 can sense mechanical vibrations caused by anultrasonic signal and produce an electrical charge at the frequency(e.g., ultrasonic frequency) of the vibrations. Additionally, thepiezoelectric layer 110 can generate an ultrasonic wave by vibrating inan oscillatory fashion that might be at the same frequency (e.g.,ultrasonic frequency) as an input current generated by an alternatingcurrent (AC) voltage applied across the piezoelectric layer 110. Itshould be appreciated that the piezoelectric layer 110 can includealmost any material (or combination of materials) that exhibitspiezoelectric properties, such that the structure of the material doesnot have a center of symmetry and a tensile or compressive stressapplied to the material alters the separation between positive andnegative charge sites in a cell causing a polarization at the surface ofthe material. The polarization is directly proportional to the appliedstress and is direction dependent so that compressive and tensilestresses results in electric fields of opposite polarizations.

Further, the PMUT device 100 comprises electrodes 106 and 108 thatsupply and/or collect the electrical charge to/from the piezoelectriclayer 110. It should be appreciated that electrodes 106 and 108 can becontinuous and/or patterned electrodes (e.g., in a continuous layerand/or a patterned layer). For example, as illustrated, electrode 106 isa patterned electrode and electrode 108 is a continuous electrode. As anexample, electrodes 106 and 108 can be comprised of almost any metallayers, such as, but not limited to, Aluminum (A)/Titanium (Ti),Molybdenum (Mo), etc., which are coupled with an on opposing sides ofthe piezoelectric layer 110. In one embodiment, PMUT device alsoincludes a third electrode, as illustrated in FIG. 10 and describedbelow.

According to an embodiment, the acoustic impedance of acoustic couplinglayer 114 is selected to be similar to the acoustic impedance of theplaten layer 116, such that the acoustic wave is efficiently propagatedto/from the membrane 120 through acoustic coupling layer 114 and platenlayer 116. As an example, the platen layer 116 can comprise variousmaterials having an acoustic impedance in the range between 0.8 to 4MRayl, such as, but not limited to, plastic, resin, rubber, Teflon,epoxy, etc. In another example, the platen layer 116 can comprisevarious materials having a high acoustic impedance (e.g., an acousticimpendence greater than 10 MRayl), such as, but not limited to, glass,aluminum-based alloys, sapphire, etc. Typically, the platen layer 116can be selected based on an application of the sensor. For instance, infingerprinting applications, platen layer 116 can have an acousticimpedance that matches (e.g., exactly or approximately) the acousticimpedance of human skin (e.g., 1.6×10⁶ Rayl). Further, in one aspect,the platen layer 116 can further include a thin layer of anti-scratchmaterial. In various embodiments, the anti-scratch layer of the platenlayer 116 is less than the wavelength of the acoustic wave that is to begenerated and/or sensed to provide minimum interference duringpropagation of the acoustic wave. As an example, the anti-scratch layercan comprise various hard and scratch-resistant materials (e.g., havinga Mohs hardness of over 7 on the Mohs scale), such as, but not limitedto sapphire, glass, MN, Titanium nitride (TiN), Silicon carbide (SiC),diamond, etc. As an example, PMUT device 100 can operate at 20 MHz andaccordingly, the wavelength of the acoustic wave propagating through theacoustic coupling layer 114 and platen layer 116 can be 70-150 microns.In this example scenario, insertion loss can be reduced and acousticwave propagation efficiency can be improved by utilizing an anti-scratchlayer having a thickness of 1 micron and the platen layer 116 as a wholehaving a thickness of 1-2 millimeters. It is noted that the term“anti-scratch material” as used herein relates to a material that isresistant to scratches and/or scratch-proof and provides substantialprotection against scratch marks.

In accordance with various embodiments, the PMUT device 100 can includemetal layers (e.g., Aluminum (Al)/Titanium (Ti), Molybdenum (Mo), etc.)patterned to form electrode 106 in particular shapes (e.g., ring,circle, square, octagon, hexagon, etc.) that are defined in-plane withthe membrane 120. Electrodes can be placed at a maximum strain area ofthe membrane 120 or placed at close to either or both the surroundingedge support 102 and interior support 104. Furthermore, in one example,electrode 108 can be formed as a continuous layer providing a groundplane in contact with mechanical support layer 112, which can be formedfrom silicon or other suitable mechanical stiffening material. In stillother embodiments, the electrode 106 can be routed along the interiorsupport 104, advantageously reducing parasitic capacitance as comparedto routing along the edge support 102.

For example, when actuation voltage is applied to the electrodes, themembrane 120 will deform and move out of plane. The motion then pushesthe acoustic coupling layer 114 it is in contact with and an acoustic(ultrasonic) wave is generated. Oftentimes, vacuum is present inside thecavity 130 and therefore damping contributed from the media within thecavity 130 can be ignored. However, the acoustic coupling layer 114 onthe other side of the membrane 120 can substantially change the dampingof the PMUT device 100. For example, a quality factor greater than 20can be observed when the PMUT device 100 is operating in air withatmosphere pressure (e.g., acoustic coupling layer 114 is air) and candecrease lower than 2 if the PMUT device 100 is operating in water(e.g., acoustic coupling layer 114 is water).

FIG. 3 is a top view of the PMUT device 100 of FIG. 1 having asubstantially square shape, which corresponds in part to a cross sectionalong dotted line 101 in FIG. 3. Layout of surrounding edge support 102,interior support 104, and lower electrode 106 are illustrated, withother continuous layers not shown. It should be appreciated that theterm “substantially” in “substantially square shape” is intended toconvey that a PMUT device 100 is generally square-shaped, withallowances for variations due to manufacturing processes and tolerances,and that slight deviation from a square shape (e.g., rounded corners,slightly wavering lines, deviations from perfectly orthogonal corners orintersections, etc.) may be present in a manufactured device. While agenerally square arrangement PMUT device is shown, alternativeembodiments including rectangular, hexagon, octagonal, circular, orelliptical are contemplated. In other embodiments, more complexelectrode or PMUT device shapes can be used, including irregular andnon-symmetric layouts such as chevrons or pentagons for edge support andelectrodes.

FIG. 4 is a simulated topographic map 400 illustrating maximum verticaldisplacement of the membrane 120 of the PMUT device 100 shown in FIGS.1-3. As indicated, maximum displacement generally occurs along a centeraxis of the lower electrode, with corner regions having the greatestdisplacement. As with the other figures, FIG. 4 is not drawn to scalewith the vertical displacement exaggerated for illustrative purposes,and the maximum vertical displacement is a fraction of the horizontalsurface area comprising the PMUT device 100. In an example PMUT device100, maximum vertical displacement may be measured in nanometers, whilesurface area of an individual PMUT device 100 may be measured in squaremicrons.

FIG. 5 is a top view of another example of the PMUT device 100 of FIG. 1having a substantially circular shape, which corresponds in part to across section along dotted line 101 in FIG. 5. Layout of surroundingedge support 102, interior support 104, and lower electrode 106 areillustrated, with other continuous layers not shown. It should beappreciated that the term “substantially” in “substantially circularshape” is intended to convey that a PMUT device 100 is generallycircle-shaped, with allowances for variations due to manufacturingprocesses and tolerances, and that slight deviation from a circle shape(e.g., slight deviations on radial distance from center, etc.) may bepresent in a manufactured device.

FIG. 6 is a top view of another example of the PMUT device 100 of FIG. 1having a substantially hexagonal shape, which corresponds in part to across section along dotted line 101 in FIG. 6. Layout of surroundingedge support 102, interior support 104, and lower electrode 106 areillustrated, with other continuous layers not shown. It should beappreciated that the term “substantially” in “substantially hexagonalshape” is intended to convey that a PMUT device 100 is generallyhexagon-shaped, with allowances for variations due to manufacturingprocesses and tolerances, and that slight deviation from a hexagon shape(e.g., rounded corners, slightly wavering lines, deviations fromperfectly orthogonal corners or intersections, etc.) may be present in amanufactured device.

FIG. 7 illustrates an example two-dimensional array 700 ofcircular-shaped PMUT devices 701 formed from PMUT devices having asubstantially circular shape similar to that discussed in conjunctionwith FIGS. 1, 2 and 5. Layout of circular surrounding edge support 702,interior support 704, and annular or ring shaped lower electrode 706surrounding the interior support 704 are illustrated, while othercontinuous layers are not shown for clarity. As illustrated, array 700includes columns of circular-shaped PMUT devices 701 that are offset. Itshould be appreciated that the circular-shaped PMUT devices 701 may becloser together, such that edges of the columns of circular-shaped PMUTdevices 701 overlap. Moreover, it should be appreciated thatcircular-shaped PMUT devices 701 may contact each other. In variousembodiments, adjacent circular-shaped PMUT devices 701 are electricallyisolated. In other embodiments, groups of adjacent circular-shaped PMUTdevices 701 are electrically connected, where the groups of adjacentcircular-shaped PMUT devices 701 are electrically isolated.

FIG. 8 illustrates an example two-dimensional array 800 of square-shapedPMUT devices 801 formed from PMUT devices having a substantially squareshape similar to that discussed in conjunction with FIGS. 1, 2 and 3.Layout of square surrounding edge support 802, interior support 804, andsquare-shaped lower electrode 806 surrounding the interior support 804are illustrated, while other continuous layers are not shown forclarity. As illustrated, array 800 includes columns of square-shapedPMUT devices 801 that are in rows and columns. It should be appreciatedthat rows or columns of the square-shaped PMUT devices 801 may beoffset. Moreover, it should be appreciated that square-shaped PMUTdevices 801 may contact each other or be spaced apart. In variousembodiments, adjacent square-shaped PMUT devices 801 are electricallyisolated. In other embodiments, groups of adjacent square-shaped PMUTdevices 801 are electrically connected, where the groups of adjacentsquare-shaped PMUT devices 801 are electrically isolated.

FIG. 9 illustrates an example two-dimensional array 900 ofhexagon-shaped PMUT devices 901 formed from PMUT devices having asubstantially hexagon shape similar to that discussed in conjunctionwith FIGS. 1, 2 and 6. Layout of hexagon-shaped surrounding edge support902, interior support 904, and hexagon-shaped lower electrode 906surrounding the interior support 904 are illustrated, while othercontinuous layers are not shown for clarity. It should be appreciatedthat rows or columns of the hexagon-shaped PMUT devices 901 may beoffset. Moreover, it should be appreciated that hexagon-shaped PMUTdevices 901 may contact each other or be spaced apart. In variousembodiments, adjacent hexagon-shaped PMUT devices 901 are electricallyisolated. In other embodiments, groups of adjacent hexagon-shaped PMUTdevices 901 are electrically connected, where the groups of adjacenthexagon-shaped PMUT devices 901 are electrically isolated. While FIGS.7, 8 and 9 illustrate example layouts of PMUT devices having differentshapes, it should be appreciated that many different layouts areavailable. Moreover, in accordance with various embodiments, arrays ofPMUT devices are included within a MEMS layer.

In operation, during transmission, selected sets of PMUT devices in thetwo-dimensional array can transmit an acoustic signal (e.g., a shortultrasonic pulse) and during sensing, the set of active PMUT devices inthe two-dimensional array can detect an interference of the acousticsignal with an object (in the path of the acoustic wave). The receivedinterference signal (e.g., generated based on reflections, echoes, etc.of the acoustic signal from the object) can then be analyzed. As anexample, an image of the object, a distance of the object from thesensing component, a density of the object, a motion of the object,etc., can all be determined based on comparing a frequency and/or phaseof the interference signal with a frequency and/or phase of the acousticsignal. Moreover, results generated can be further analyzed or presentedto a user via a display device (not shown).

FIG. 10 illustrates a pair of example PMUT devices 1000 in a PMUT array,with each PMUT sharing at least one common edge support 1002. Asillustrated, the PMUT devices have two sets of independent lowerelectrode labeled as 1006 and 1026. These differing electrode patternsenable antiphase operation of the PMUT devices 1000, and increaseflexibility of device operation. In one embodiment, the pair of PMUTsmay be identical, but the two electrodes could drive different parts ofthe same PMUT antiphase (one contracting, and one extending), such thatthe PMUT displacement becomes larger. While other continuous layers arenot shown for clarity, each PMUT also includes an upper electrode (e.g.,upper electrode 108 of FIG. 1). Accordingly, in various embodiments, aPMUT device may include at least three electrodes.

FIGS. 11A, 11B, 11C, and 11D illustrate alternative examples of interiorsupport structures, in accordance with various embodiments. Interiorsupports structures may also be referred to as “pinning structures,” asthey operate to pin the membrane to the substrate. It should beappreciated that interior support structures may be positioned anywherewithin a cavity of a PMUT device, and may have any type of shape (orvariety of shapes), and that there may be more than one interior supportstructure within a PMUT device. While FIGS. 11A, 11B, 11C, and 11Dillustrate alternative examples of interior support structures, itshould be appreciated that these examples or for illustrative purposes,and are not intended to limit the number, position, or type of interiorsupport structures of PMUT devices.

For example, interior supports structures do not have to be centrallylocated with a PMUT device area, but can be non-centrally positionedwithin the cavity. As illustrated in FIG. 11A, interior support 1104 ais positioned in a non-central, off-axis position with respect to edgesupport 1102. In other embodiments such as seen in FIG. 1B, multipleinterior supports 1104 b can be used. In this embodiment, one interiorsupport is centrally located with respect to edge support 1102, whilethe multiple, differently shaped and sized interior supports surroundthe centrally located support. In still other embodiments, such as seenwith respect to FIGS. 11C and 11D, the interior supports (respectively1104 c and 1104 d) can contact a common edge support 1102. In theembodiment illustrated in FIG. 11D, the interior supports 1104 d caneffectively divide the PMUT device into subpixels. This would allow, forexample, activation of smaller areas to generate high frequencyultrasonic waves, and sensing a returning ultrasonic echo with largerareas of the PMUT device. It will be appreciated that the individualpinning structures can be combined into arrays.

FIG. 12 illustrates an embodiment of a PMUT array used in an ultrasonicfingerprint sensing system 1250. The fingerprint sensing system 1250 caninclude a platen 1216 onto which a human finger 1252 may make contact.Ultrasonic signals are generated and received by a PMUT device array1200, and travel back and forth through acoustic coupling layer 1214 andplaten 1216. Signal analysis is conducted using processing logic module1240 (e.g., control logic) directly attached (via wafer bonding or othersuitable techniques) to the PMUT device array 1200. It will beappreciated that the size of platen 1216 and the other elementsillustrated in FIG. 12 may be much larger (e.g., the size of ahandprint) or much smaller (e.g., just a fingertip) than as shown in theillustration, depending on the particular application.

In this example for fingerprinting applications, the human finger 1252and the processing logic module 1240 can determine, based on adifference in interference of the acoustic signal with valleys and/orridges of the skin on the finger, an image depicting epi-dermis and/ordermis layers of the finger. Further, the processing logic module 1240can compare the image with a set of known fingerprint images tofacilitate identification and/or authentication. Moreover, in oneexample, if a match (or substantial match) is found, the identity ofuser can be verified. In another example, if a match (or substantialmatch) is found, a command/operation can be performed based on anauthorization rights assigned to the identified user. In yet anotherexample, the identified user can be granted access to a physicallocation and/or network/computer resources (e.g., documents, files,applications, etc.)

In another example, for finger-based applications, the movement of thefinger can be used for cursor tracking/movement applications. In suchembodiments, a pointer or cursor on a display screen can be moved inresponse to finger movement. It is noted that processing logic module1240 can include or be connected to one or more processors configured toconfer at least in part the functionality of system 1250. To that end,the one or more processors can execute code instructions stored inmemory, for example, volatile memory and/or nonvolatile memory.

FIG. 13 illustrates an integrated fingerprint sensor 1300 formed bywafer bonding a CMOS logic wafer and a MEMS wafer defining PMUT devices,according to some embodiments. FIG. 13 illustrates in partial crosssection one embodiment of an integrated fingerprint sensor formed bywafer bonding a substrate 1340 CMOS logic wafer and a MEMS waferdefining PMUT devices having a common edge support 1302 and separateinterior support 1304. For example, the MEMS wafer may be bonded to theCMOS logic wafer using aluminum and germanium eutectic alloys, asdescribed in U.S. Pat. No. 7,442,570. PMUT device 1300 has an interiorpinned membrane 1320 formed over a cavity 1330. The membrane 1320 isattached both to a surrounding edge support 1302 and interior support1304. The membrane 1320 is formed from multiple layers.

What has been described above includes examples of the subjectdisclosure. It is, of course, not possible to describe every conceivablecombination of components or methodologies for purposes of describingthe subject matter, but it is to be appreciated that many furthercombinations and permutations of the subject disclosure are possible.Accordingly, the claimed subject matter is intended to embrace all suchalterations, modifications, and variations that fall within the spiritand scope of the appended claims.

In particular and in regard to the various functions performed by theabove described components, devices, circuits, systems and the like, theterms (including a reference to a “means”) used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., a functional equivalent), even though not structurallyequivalent to the disclosed structure, which performs the function inthe herein illustrated exemplary aspects of the claimed subject matter.

The aforementioned systems and components have been described withrespect to interaction between several components. It can be appreciatedthat such systems and components can include those components orspecified sub-components, some of the specified components orsub-components, and/or additional components, and according to variouspermutations and combinations of the foregoing. Sub-components can alsobe implemented as components communicatively coupled to other componentsrather than included within parent components (hierarchical).Additionally, it should be noted that one or more components may becombined into a single component providing aggregate functionality ordivided into several separate sub-components. Any components describedherein may also interact with one or more other components notspecifically described herein.

In addition, while a particular feature of the subject innovation mayhave been disclosed with respect to only one of several implementations,such feature may be combined with one or more other features of theother implementations as may be desired and advantageous for any givenor particular application. Furthermore, to the extent that the terms“includes,” “including,” “has,” “contains,” variants thereof, and othersimilar words are used in either the detailed description or the claims,these terms are intended to be inclusive in a manner similar to the term“comprising” as an open transition word without precluding anyadditional or other elements.

Thus, the embodiments and examples set forth herein were presented inorder to best explain various selected embodiments of the presentinvention and its particular application and to thereby enable thoseskilled in the art to make and use embodiments of the invention.However, those skilled in the art will recognize that the foregoingdescription and examples have been presented for the purposes ofillustration and example only. The description as set forth is notintended to be exhaustive or to limit the embodiments of the inventionto the precise form disclosed.

What is claimed is:
 1. A Piezoelectric Micromachined UltrasonicTransducer (PMUT) device comprising: a substrate; an edge supportstructure connected to the substrate; a membrane connected to the edgesupport structure such that a cavity is defined between the membrane andthe substrate, the membrane configured to allow movement at ultrasonicfrequencies, the membrane comprising: a piezoelectric layer; and firstand second electrodes coupled to opposing sides of the piezoelectriclayer; and an interior support structure disposed within the cavity andconnected to the substrate and the membrane.
 2. The PMUT device of claim1, further comprising: a second interior support structure disposedwithin the cavity and connected to the substrate and the membrane. 3.The PMUT device of claim 1, wherein the interior support structure isnon-centrally positioned within the cavity.
 4. The PMUT device of claim1, wherein the first electrode defines a continuous layer.
 5. The PMUTdevice of claim 1, wherein the first electrode is a patterned layer. 6.The PMUT device of claim 1, the membrane further comprising: amechanical support layer connected to the first electrode.
 7. The PMUTdevice of claim 6, wherein the mechanical support layer defines acontinuous layer.
 8. The PMUT device of claim 6, wherein the mechanicalsupport layer is a patterned layer.
 9. The PMUT device of claim 1,wherein the piezoelectric layer defines a continuous layer.
 10. The PMUTdevice of claim 1, wherein the piezoelectric layer is a patterned layer.11. The PMUT device of claim 1, wherein the second electrode extendsinto the cavity and defines an area between the edge support structureand the interior support structure.
 12. The PMUT device of claim 1,wherein the interior support structure is connected to the piezoelectriclayer of the membrane.
 13. The PMUT device of claim 1, wherein the PMUTdevice is substantially circular such that the edge support structureand the membrane are substantially circular.
 14. The PMUT device ofclaim 1, wherein the PMUT device is substantially square-shaped suchthat the edge support structure and the membrane are substantiallysquare-shaped.
 15. The PMUT device of claim 1, wherein at least one ofthe first electrode and the second electrode is electrically coupledthrough the interior support structure.
 16. The PMUT device of claim 1,the membrane further comprising: a third electrode coupled to thepiezoelectric layer on an opposing side of the piezoelectric layer asthe first electrode.
 17. The PMUT device of claim 1, wherein the edgesupport structure is connected to an electric potential.
 18. The PMUTdevice of claim 1, wherein the substrate comprises a CMOS logic wafer.19. A Piezoelectric Micromachined Ultrasonic Transducer (PMUT) arraycomprising: a plurality of PMUT devices, wherein at least one PMUTdevice of the plurality of PMUT devices comprises: a substrate; an edgesupport structure connected to the substrate, wherein the edge supportstructure is connected to an electric potential; a membrane connected tothe edge support structure such that a cavity is defined between themembrane and the substrate, the membrane configured to allow movement atultrasonic frequencies, the membrane comprising: a piezoelectric layer;first and second electrodes coupled to opposing sides of thepiezoelectric layer; and a mechanical support layer connected to thefirst electrode; and an interior support structure disposed within thecavity and connected to the substrate and the membrane.
 20. An imagesensing system comprising: a plurality of Piezoelectric MicromachinedUltrasonic Transducer (PMUT) devices, wherein at least one PMUT deviceof the plurality of PMUT devices comprises: a substrate; an edge supportstructure connected to the substrate; a membrane connected to the edgesupport structure such that a cavity is defined between the membrane andthe substrate, the membrane configured to allow movement at ultrasonicfrequencies, the membrane comprising: a piezoelectric layer; first andsecond electrodes coupled to opposing sides of the piezoelectric layer;and a mechanical support layer connected to the first electrode; and aninterior support structure disposed within the cavity and connected tothe substrate and the membrane; and control logic electrically coupledto the plurality of PMUT devices, the control logic for sensing animage.